1. Field of the Invention
The present invention relates to a microactuator for finely vibrating a structure by an electrostatic repulsive force, and a method for controlling the resonant frequency thereof.
2. Description of the Related Art
A microactuator using an electrostatic force may be classified into one using an electrostatic attractive force and the other using an electrostatic repulsive force.
A microactuator using the electrostatic attractive force is disclosed in U.S. Pat. No. 5,025,346, and shown in FIG. 1. On an inertial member 10, moving electrodes 11 are formed to be interposed between and adjacent to fixed electrodes 12. The microactuator is driven by an electrostatic attractive force between the moving electrodes 11 and the fixed electrodes 12. However, the resonant frequency of the inertial member 10 cannot be changed.
Another microactuator using the electrostatic attractive force is disclosed in "A Micromachined, single-crystal silicon, tunable resonator," J. J. Yao and N. C. MacDonald in J. Micromech. Microeng., Vol. 6, 1996, pp. 257-264. In this microactuator, if a voltage applied between the flat-shaped inertial member and a bottom electrode is increased in order to generate the electrostatic attractive force therebetween, the resonant frequency of the inertial member tends to be reduced. If the electrostatic attractive force is increased, the inertial member adheres to the bottom electrode.
A method for driving an inertial member using the electrostatic repulsive force is disclosed in "Electrostatic Comb Drive Levitation and Control Method", J. Microelectromech. Sys., Vol. 1, No. 4 (1992) pp170-178. According to the method, as shown in FIG. 2, an inertial member 23 supported from a base 21 by a spring 22 is vertically driven by an electrostatic repulsive force formed between a substrate 20 and the inertial member 23.